How to Make Bluing Tanks
What is Hot Salt Bluing?
Hot salt bluing is a finish for firearms which creates a colorful layer that prevents rusting and holds oil. Bluing itself is actually a type of rust known as black rust or iron trioxide. Unlike the typical red rust (iron dioxide), black rust has a tighter molecular structure which isn’t flakey and can be used as a protective coating.
Much of the bluing process is proper timing and babysitting the temperature of the tanks. Without constant temperature monitoring, the bluing tanks could get too hot and ruin the salts or degreasing chemicals. It is an all-day process which consists of several steps and takes a lot of attention to detail.
How to Make Bluing Tanks
Before we moved locations, we didn’t have enough workspace to offer hot salt bluing. Now that we have settled into our new shop and have enough room, we’ve decided to begin offering bluing services. But first, we needed the equipment. We searched Brownells, but much to our dismay, each stainless steel bluing tank cost around $200. And that didn’t even include the stands which came in at $150 each. Nor did it include the burners which cost between $200 and $300 each!
So, as we do with most things that cost too much, we decided to build them ourselves. Taking the dimensions of the tanks from the Brownells website, we purchased the necessary materials from Coyote Steel in Eugene. Using Brownells as inspiration for the design, we welded the sheet metal into rectangular tanks, welded the stands together, and built our own burners.
The hot salt bluing process requires six tanks in total. This would’ve been thousands of dollars in equipment. But instead, we decided to make our own, and we saved a ton of money. To build the six tanks (and two extras), we spent $75 on sheet metal and $50 in total for the stands. We also didn’t have to pay for shipping!
Six Bluing Tanks
Hot salt bluing done right uses six tanks—each with a different purpose and processes. Every tank is made from stainless steel except the hot salt tank.
TANK #1 DEGREASER
Electric Prototype for Degreaser Tank
This tank is used to clean the surface of the metal. It must be warmed to 170 degrees. We made two of these tanks. One was a standard tank with a small propane burner which we made from a black iron pipe with holes drilled in it. Using a regulator, we hooked the burner up to the propane tank.
The second was our first electric bluing tank prototype. This one worked successfully and uses an electric coil inside the tank to heat the water to the proper temperature.
TANK #2 COLD WATER RINSE (FOR DEGREASER)
This tank contains constantly circulating cold water which rinses off the degreaser. Without this tank, the degreaser can inhibit the function of the bluing salts on the gun. It is important to remove all of the degreaser before starting the hot salt process.
TANK #3 HOT SALT
This tank contains the caustic salt bluing solution. Because it needs to be at 295 degrees (Fahrenheit), the hot salt tank requires a large burner. We made this one in the same way as the propane degreaser tank.
Propane Burner
This is the only tank that isn’t stainless steel. Because the bluing salts will displace and deposit non-ferrous metals (i.e. copper, nickel, chrome, and other metal alloys) onto the ferrous metals (i.e. the gun), the tank cannot be made of stainless steel. Otherwise, the gun will have weird copper spots on it. But the hot salt process will actually blue the tank itself. So we don’t have to worry about red rust!
TANK #4 SECOND COLD WATER RINSE (FOR SALTS)
A second, circulating cold water tank is necessary to remove the bluing salts and stop them from acting on the metal. It is important to have a separate cold-water tank for both the salts and degreaser. Otherwise, the salts will contaminate the degreaser. Cross contamination will led to poor bluing results.
TANK #5 BOILING WATER RINSE
After the cold water rinse, the boiling water tank—set to 212 degrees (Fahrenheit)—is used to rinse the gun a second time. This ensures that any remaining bluing salts are dissolved off of every nook and cranny of the gun. This tank uses the same small propane burner as the degreaser tank.
Electric Bluing Tank Prototype: Notice how the water is boiling near the coil but not in the rest of the tank
We also attempted to make an electric version of this tank. While we were able to get the entire tank to heat up, we were only able to get the water around the electric coil to boil. We have some theories and solutions but won’t have time to address those problems until our first round of bluing is complete.
TANK #6 WATER DISPLACING OIL
This is the final tank in the bluing process. The water displacing oil removes all the water from the gun and seals the bluing.
Electric Bluing Tank Prototype
We are excited to have our hot salt bluing tanks up and running! And we are even more excited to continue prototyping our electric bluing tank idea. Not only will bluing with electric burners be cheaper, but it will also be more time-efficient.
The main problem of bluing using propane is the amount time it takes to setup and the constant observation and regulation of temperature. With an electric set up, we would be able to automate the temperature control. We wouldn’t have to add water or more heat to keep the temperature right. We could turn it on and walk away—letting the computer do all of the work.
